This invention relates to a method of producing a racket frame in which a fiber reinforced thermosetting resin is molded into a racket frame.
Composite racket frames generally include a shell made of a plurality of layers of thermorsetting resin-impregnated woven glass fibers or graphite fibers and a foam core intimately bonding with the shell. During the processing of such composite structure it usually need an internal pressure to force the shell to closely contact with the inner wall of the mold cavity to take the shape thereof. There are two methods of generating a sufficient internal pressure, i.e. direct method (blow molding) and indirect method (foam molding). In the first method the shell side is forced by the compressed air to closely contact with the inner wall of the mold cavity to take a predetermined shape. The hollow central portion is then provided with a foamable thermoplastic composition which will then be foamed and cured therein by heating. This additional step may incur further expenses during processing.
In the second method, a plurality of resin-impregnated woven fibers layers are wrapped around a foamable core composition and then put into a mold cavity for molding. When heating the foaming agent activates the core composition to generate a pressure to produce a desired molded shape after curing. Although the latter method is more simpler than the former one, the temperature for gelling and curing the resin-impregnated fibers and for foaming the thermoplastic resin are not the same. Therefore the pressure generated are not controllable and the resin from the core may penetrate into the shell layers, thereby destorying the orientation of the fiber as well as the reinforcement thereof.